Field of Invention
The present invention relates to the technical field of a device for contaminated soil remediation, and more particularly to an indirect thermal desorption device with two-section screw conveyors.
Description of Related Arts
Soil, which is an important part of human ecological environment, is an important natural source for the existence of human beings. With the development of social technology and economy and the continuous improvements of people's living standard and health level, there are higher requirements for green environment and the treatment of environmental pollution becomes an important issue for urban construction. With the regulation on industrial structures, a plurality of industrial enterprises previously located on the central areas of multiple cities are closed down or relocated, and large quantities of severe contaminated soil are left, including a large quantity of organic contaminated soil. The severe contaminated soil will pollute the atmosphere and water in the surroundings and has a harmful effect on people's life and health. The contaminated sites are not suitable for being put into new applications until being remediated, so the remediation of contaminated soil has become an important part of environmental protection.
Soil remediation has always been a difficult and hot research topic in the world. Some universities and scientific research departments in China have realized the policy orientation and future requirements of the country and foreseen a large progress space of the industry in the future, and related works have been done in the technical and management field.
Thermal desorption technique is one of the main remediation techniques in the remediation of organic contaminated soil or mercury contaminated soil. The thermal desorption technique utilized direct or indirect heat-exchange heating to make the contaminated components in the soil reach a high enough temperature to evaporate and be separated from the soil media. The separated contaminated components are further treated by incineration, adsorption or chemical reaction. The thermal transmission medium in the thermal desorption device is usually gas, combustion gas, insert gas, high-temperature gas, thermal oil or molten salt and etc. The thermal desorption process is a physical process for the contaminated components in the soils converting into a steam phase from the solid phase or the liquid phase.
A first Chinese patent application with a publication number CN103203355A discloses an ex-situ thermal desorption treatment method for contaminated soil. The contaminated soil is sieved, crushed and piled up. The mound of the contaminated soil has a uniform thickness. A static pressure chamber is provided below the contaminated soil and the contaminated soil is covered by a sealed insulation layer. A main extraction steam tube is provided on a covered surface of the sealed insulation layer, and switching valves are provided on parallel tubes. The object of the patent application CN103203355A is to solve the problems of the high consumption and waste of energy of the thermal treatment technique during the remediation and regeneration process of the contaminated soil.
A second Chinese patent application with a publication number CN103341486A discloses an electromagnetic thermal desorption system for contaminated soil, comprising: a drum type electromagnetic heat absorber, an electromagnetic heating control system, a drum speed control system and a heat exchanger and an exhaust gas purification system. The object of the patent application CN103341486A is to ensure that organic contaminants volatilized from the contaminated soil are brought out of the drum type electromagnetic heat absorber in time. The exhaust gas is treated by heat exchange with cold air and drops the temperature thereof, and the exhaust passes through an exhaust outlet to enter a wet precipitator in the exhaust purification system, and then enter an activated carbon absorber.
A third Chinese patent application with a publication number CN104096709A discloses a thermal desorption device for remediation of mercury contaminated soil. The device comprises: a feed system, a rotary kiln heating system, a dust removing system, a cooling and condensing system, an exhaust gas filtration system, a gas discharge system, a liquid condensate collection system, a precipitation filtration system, a soil cooling system and a discharge system. The patent application CN104096709A is specially designed for mercury contaminated soil, so as to remediate soil contaminated by mercury.
The three patent applications mentioned above all perform part improvement on the conventional thermal desorption technique. The patent application with the publication number CN103203355A is capable of partially decreasing the power consumption, but has disadvantages of long remediation cycle and insufficient remediation. The patent application with the publication number CN103341486A adopts a secondary energy source for heating, and has disadvantages of high disposal cost and difficulty in sealing the drum. The patent application with the publication number CN104096709A adopts the rotary kiln as a main thermal desorption device, but the direct heating adopted thereby needs a secondary treatment of the exhaust gas, the device is complicated, the transportation and installation are inconvenient, and has shortcomings of high operation cost and having risks of secondary contamination.